1. Field of the Invention
This invention relates to sealed bearing rock bits.
More particularly, this invention relates to sealed bearing rock bits with a means to circulate lubricating grease from a rock bit reservoir system to bearings defined between one or more rotary cones and their respective journals.
2. Description of the Prior Art
Down through the years in the drilling industry there have been various methods incorporated to lubricate rock bits as they operate in a borehole.
The following prior art patents all relate to a means to lubricate a rotary cone rock bit. This prior art includes the following U.S. Pat. Nos.: 1,487,319 (O. Duda/3-18-24); 2,174,102 (A. C. Catland/9-26-39); 3,244,459 (J. E. Ortloff/4-5-66); 3,251,634 (D. W. Dareing/5-17-66); 3,463,270 (H. P. O. Lundstrom et al/8-26-69); 3,841,422 (M. L. Crow/10-15-74); 3,844,364 (M. L. Crow/10-29-74); 4,167,219 (R. W. McQueen/9-11-79), 4,181,185 (W. S. Keller et al/1-1-80); and 4,183,416 (D. F. Walters/1-15-80).
U.S. Pat. No. 1,487,319 describes a system to apply pressure to a lubricating reservoir section above a rock bit. The lubricant circulates through the bearing surfaces of the rock bit into the borehole as the rock bit works in the hole. An axially aligned roller, mounted in a sub section above the bit, contacts the borehole surface. The roller includes an eccentric vane type pump which is driven by the roller as it contacts the wall of the borehole during operation of the rock bit. Each revolution of the roller drives a vane, riding in an eccentric track, which supplies fluid under pressure to one side of a piston near the top of the oil reservoir in the sub pipe section mounted to the rock bit. Pressure on top of the piston drives lubricant within the reservoir above the rock bit to force lubricating fluids through the bearing surfaces of the rotary cone rock bit attached to the sub. The foregoing pressurizing system is housed in a separate sub section that is attached to a rock bit and is not integral with the rotary cone bit nor is the rock bit a sealed bearing rock bit, the lubricant being free to flow through the bearing surfaces and out of the bit as it works in a borehole.
U.S. Pat. No. 2,174,102 describes a sealed bearing rock bit with internal lubricating fluid circulation means within the bit. A cam surface is provided within the bearing surfaces of a rotary cone mounted to a journal of a rock bit. A check valve means is retained radially within the journal bearing of the rotary cone. Rotation of the cone drives the stem of a check valve up a ramp in the cone bearing surface to allow lubricant, under pressure from a reservoir centrally positioned in the journal, to pass to the bearing surfaces.
Journal bearings for rock bits are subjected to severe shock and bending loads under downhole conditions in a drilling operation, hence, the rock bits must necessarily be extremely rugged. This particular patent illustrates a relatively large lubricant chamber centrally positioned within the journal bearing to act as a lubricant reservoir. The chamber communicates with radially directed passages to move lubricant from the central pressurized chamber to the bearing surfaces. It is generally undesirable to interrupt the integrity of a journal bearing for a rock bit by providing large passages either axially or radially in the journal. Catastrophic journal failures, due to heavy shock and stresses, are more likely to occur in this type of design.
U.S. Pat. No. 3,244,459 describes yet another rock bit with an internal lubrication system. This patent describes a rather large axially aligned hole through the center of a journal bearing with a piston fitted within the bore in the journal, backed up by a spring. The piston is driven by a cam connected to the cone that rides against an end of the piston. Rotation of the cone drives the piston axially back and forth, thereby pumping lubricant from a reservoir in the leg of the rock bit to the bearing surfaces. Point contact of the cam surface with the piston pump causes relatively high unit loading which would be detrimental to the smooth, relatively drag-free operation of the rock bit.
This patent is somewhat similar to the '102 patent described above in that it has a very large axially aligned hole through the center of the journal, thereby weakening the journal by subjecting it to fracture type failures under downhole working conditions.
U.S. Pat. No. 4,183,416 describes a sealed bearing rotary cone rock bit having a rotating cone with an axially aligned, inwardly extending spiral screw that interfits within an axially aligned chamber in the journal bearing of the rotary cone. The rotary cone, as it rotates on a borehole bottom, tends to influence migration of lubricant from a reservoir through the bearings and back to the reservoir in a lubricant pumping circulation system. Again, this bit has a relatively large hole bored axially through the center of the journal bearing, thus providing a fracture path under load conditions.
This patent however is not a positive displacement pump and its effectiveness to move lubricant is doubtful. It is generally known that grease for lubrication of rock bits is highly viscous and does not "flow" as does a less viscous oil.
U.S. Pat. Nos. 4,181,185 and 4,183,416 similarly are not positive displacement type pumps and serve only to influence grease migration. The basic principle is fundamentally different from the present invention where highly viscous grease is forced from a grease reservoir to the bearing surfaces and back to the reservoir.